Liquid crystal display device

ABSTRACT

A pixel of a liquid crystal display device includes a scan line, a signal line, a TFT, a lower electrode, and an upper electrode arranged thereon with a protection film interposed therebetween, in which the upper electrode includes a plurality of branch electrode parts electrically connected in common, and a gap part between the branch electrode parts. The upper electrode includes a region in which a ratio of a width of the gap part to a width of the branch electrode part that is adjacent to the gap part is different, and includes both of a region in which a light transmittance increases and a region in which the light transmittance decreases with respect to a change in the ratio.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2010-016795, filed on Jan. 28, 2010, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device. Morespecifically, the present invention relates to an electrode shape of afringe field switching (FFS) type liquid crystal display device.

2. Description of Related Art

In recent years, in substitution for a conventional cathode-ray tube,new display devices having a thin flat-type display panel usingprinciples of liquid crystals, electroluminescence or the like have beenused a lot. A liquid crystal display device which represents these newdisplay devices has characteristics in that it can be driven with a lowpower voltage, in addition to its thinness and lightness. The liquidcrystal display device includes a liquid crystal layer disposed betweentwo substrates. One substrate is an array substrate forming a displayarea in which a plurality of pixels are arranged in matrix, and theother substrate is a color filter substrate.

In particular, in a thin film transistor (TFT)-type liquid crystaldisplay device, a TFT which is a switching element is provided in eachpixel on the array substrate, and each pixel is able to independentlycarry a voltage to drive a liquid crystal layer, thereby making itpossible to achieve the display of high quality with less crosstalk.Each pixel includes a scan line (gate line) that controls ON/OFF of theTFT, and a signal line (source line) for inputting image data. Eachpixel typically corresponds to an area surrounded by the scan line andthe signal line.

An In-Plane switching (IPS)-type liquid crystal display device has onearray substrate on which a plurality of pixel electrodes and opposedelectrodes (common electrodes) are alternately arranged, so as to applya substantially-horizontal electric field to the substrate surface fordisplay. The IPS type liquid crystal display device has better viewangle property compared with a typical TN (Twisted Nematic) type.However, the conventional IPS-type liquid crystal display device has asmaller light transmittance compared with the typical TN type.

As a system in which this defect is improved, a fringe field switching(FFS) system has been suggested (for example, Japanese Unexamined PatentApplication Publication Nos. 11-202356, 2008-197343). The FFS-typeliquid crystal display device is the system of achieving the display byapplying a fringe electric field (an oblique electric field includingboth components of a horizontal electric field and a vertical electricfield) to a liquid crystal layer. In the FFS-type liquid crystal displaydevice, the pixel electrode and the opposed electrode are formed on onearray substrate as is similar to the IPS system. However, the pixelelectrode and the opposed electrode are overlapped with each other withan insulation film interposed therebetween. Typically, the lowerelectrode has a plate-like shape (the lower electrode may be a pluralityof brunch-like electrodes). Furthermore the upper electrode includes aplurality of branch electrode parts electrically connected in common,and gap parts each of which being interposed between the branchelectrode parts.

The pixel electrode may be formed either in the lower electrode or theupper electrode. In the transmission type, the pixel electrode and theopposed electrode are both formed of transparent conductive films. Inthe reflective type, the upper electrode may be formed of a transparentconductive film and the lower electrode may be formed of a conductivefilm having high reflectance rate. The liquid crystal layer is driven bythe fringe electric field between the upper electrode and the lowerelectrode in the FFS system, thereby making it possible to drive theliquid crystal layer on the branch electrode parts and gap parts of theupper electrode. For example, in the transmission type, the pixelelectrode and the opposed electrode are formed of transparent conductivefilms. Thus, the FFS system achieves improved light transmittance thanthe IPS system that transmits little light on the pixel electrode andthe opposed electrode.

SUMMARY OF THE INVENTION

However, the present inventors have found a problem as follows. In theconventional FFS system, the widths of the gap parts and the branchelectrode parts of the upper electrode relate to an electric fieldapplied to a liquid crystal layer, and give an influence on the lighttransmittance of a pixel. Accordingly, the problem is that, when thereare produced variations in dimension of the width of the gap parts orthe branch electrode parts of the upper electrode in an exposing processor an etching process or the like in an array manufacturing process, thevariations may be recognized as display unevenness of the liquid crystaldisplay device.

The present invention has been made in order to overcome the problem asabove, and in particular, aims to provide an FFS-type liquid crystaldisplay device with fewer display unevenness due to variations indimension of the width of the gap parts or the branch electrode parts ofthe upper electrode.

A first exemplary aspect of the present invention is a liquid crystaldisplay device including: a pair of substrates; a liquid crystal layerthat is sealed between the substrates; and a display area including aplurality of pixels arranged therein in matrix on one of the substrates,the pixels being defined by scan lines and signal lines that cross withthe scan lines, in which each of the pixels includes a switchingelement, a lower electrode, and an upper electrode that is arranged onthe lower electrode with an insulation film interposed therebetween, theupper electrode includes a plurality of branch electrode partselectrically connected in common, and a gap part between the branchelectrode parts, the upper electrode includes a region in which a ratioof a width of the gap part to a width of the branch electrode part thatis adjacent to the gap part is different, and the upper electrodeincludes both of a region in which a light transmittance increases and aregion in which the light transmittance decreases with respect to achange in the ratio.

An FFS-type liquid crystal display device according to the presentinvention makes it possible to reduce display unevenness due tovariations in dimension of the width of the gap parts or the branchelectrode parts of the upper electrode.

The above and other objects, features and advantages of the presentinvention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plane view schematically showing a liquid crystal displaydevice according to a first exemplary embodiment;

FIG. 2 is an enlarged plane view showing a pixel of a display area ofthe liquid crystal display device according to the first exemplaryembodiment;

FIG. 3 is a cross-sectional view taken along the line of FIG. 2;

FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 2;

FIG. 5 is a plane view showing a main part of an upper electrode of theliquid crystal display device according to the first exemplaryembodiment;

FIG. 6 is a calculation diagram showing one example of relations betweenlight transmittances and ratios of a width of a gap part to a width of abranch electrode part that is adjacent to the gap part in the liquidcrystal display device according to the first exemplary embodiment;

FIG. 7 is a view showing relations between light transmittances andratios of a width of a gap part to a width of a branch electrode partthat is adjacent to the gap part in the liquid crystal display deviceaccording to the first exemplary embodiment;

FIG. 8 is a view showing relations between light transmittances andratios when the ratios shown in FIG. 7 vary;

FIG. 9 is an enlarged plane view showing a pixel of a display area in aliquid crystal display device according to a second exemplaryembodiment;

FIG. 10 is an enlarged plane view showing a pixel of a display area in aliquid crystal display device according to a third exemplary embodiment;

FIG. 11 is an enlarged plane view showing a pixel of a display area in aliquid crystal display device according to a fourth exemplaryembodiment;

FIG. 12 is an enlarged plane view showing a pixel of a display area in aliquid crystal display device according to a fifth exemplary embodiment;

FIG. 13 is a plane view showing an upper electrode and a lower electrodeof a liquid crystal display device according to a sixth exemplaryembodiment; and

FIG. 14 is a plane view showing an upper electrode and a lower electrodeof a liquid crystal display device according to a seventh exemplaryembodiment.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of a display device of the presentinvention will be described in detail with reference to the drawings.Throughout the drawings, the same or similar parts are denoted by thesame reference symbols, and overlapping description will be omitted asappropriate.

First Exemplary Embodiment

First, a configuration of a liquid crystal display device will bedescribed in brief. FIG. 1 is a plane view schematically showing aliquid crystal display device according to a first exemplary embodiment.

In a display area 50 of a liquid crystal display device 100, a pluralityof pixels 30 are arranged in matrix. The liquid crystal display device100 includes an array substrate 10, a color filter substrate 20 and soon. The array substrate 10 includes a scan line, a signal line, a TFT, apixel electrode and the like forming the pixel 30 formed therein. Thecolor filter substrate 20 is arranged opposite to the array substrate 10with a liquid crystal layer interposed therebetween, and includes acolor filter, a light-shielding film (black matrix) and the like formedtherein. In the FFS-type liquid crystal display device 100, an opposedelectrode of a reference potential is also formed on the array substrate10.

The array substrate 10 includes the display area 50 and a frame area 55which is provided in the outer periphery of the display area 50 on atransparent substrate 1 such as glass or plastic. In the frame area 55,a scan line drive circuit 60 and a signal line drive circuit 65 aremounted by a COG (Chip On Glass) mounting technique. Further, in the endof the transparent substrate 1, a plurality of terminals (not shown) arearranged. In order to supply various voltages, clocks, image data or thelike to the scan line drive circuit 60 and the signal line drive circuit65, the plurality of terminals are connected to flexible substrates 70and 75 connected to an external circuit.

In FIG. 1, there are actually provided a plurality of lines includinglead-out lines of scan lines or signal lines extending from the displayarea 50 to the frame area 55, which are provided with the scan linedrive circuit 60 or the signal line drive circuit 65, and input linesconnecting between input parts of the scan line drive circuit 60 and thesignal line drive circuit 65 and the plurality of terminals provided inthe end of the transparent substrate 1 to connect to the flexiblesubstrates 70 and 75. But, these lines are not shown for the sake ofsimplicity.

Further, since a small-sized panel has relatively a small number oflines in total, a drive circuit in which the scan line drive circuit 60and the signal line drive circuit 65 are integrated is often used insuch a small-sized panel. At the same time, the flexible substrates 70and 75 are often used in a single plate.

FIG. 2 is an enlarged plane view showing a pixel of the display area ofthe liquid crystal display device according to the first exemplaryembodiment. FIG. 3 is a cross-sectional view taken along the line ofFIG. 2. FIG. 4 is a cross-sectional view taken along the line IV-IV ofFIG. 2.

As shown in FIGS. 2, 3, and 4, on the transparent substrate 1 made ofglass, plastic, or the like, scan lines 2 formed of metal (e.g., Al, Cr,Mo, Ti, Ta, W, Ni, Cu, Au, Ag), or alloy or laminated films thereof, andcommon lines 21 that supplies a reference potential to an opposedelectrode are formed in the same layer. Then, a gate insulation film 3made of an oxide film, a nitride film or the like is formed thereon. Ona part of the gate insulation film 3 on the scan line 2, a semiconductorfilm 4 and an ohmic contact film 41 into which impurities are injectedare laminated. Further, signal lines 5 made of metal (e.g., Al, Cr, Mo,Ti, Ta, W, Ni, Cu, Au, Ag), or alloy or laminated films thereof isformed so as to cross the scan lines 2. Further, source electrodes 51and drain electrodes 52 are formed in the same layer as the signal lines5 so as to overlap with the ohmic contact film 41. The ohmic contactfilm 41 which is located between the source electrode 51 and the drainelectrode 52 is removed, and serves as a channel part. The scan line 2which is below the channel part serves as a gate electrode, where a TFTwhich is a switching element is formed.

In the first exemplary embodiment, plate-like lower electrodes 6 arepixel electrodes. In the transmission type, the lower electrodes 6 areformed of a transparent conductive film such as ITO (Indium Tin Oxide)or the like. In the reflective type, the lower electrodes 6 are formedof metal such as Al, Ag, Pt, or alloy or laminated films thereof, andthe surface of the lower electrodes 6 are formed of a conductive filmwith high reflectance rate. The lower electrode 6 is directly formed onand electrically connected to the drain electrode 51. Note that thelower electrode 6 may be formed under and electrically connected to thedrain electrode 51.

On the signal line 5, the source electrode 51, the drain electrode 52,and the lower electrode 6, a protection film 7 that is formed of aninsulation film such as an oxide film, a nitride film, or an organicresin film, or laminated films thereof is formed.

An upper electrode 8 which is the opposed electrode is formed on theprotection film 7, which is formed on the area of the lower electrode 6which is the pixel electrode. As shown in FIG. 2, the upper electrode 8which is formed of a transparent conductive film such as ITO includes aplurality of gap parts 81 having no transparent conductive films, and aplurality of branch electrode parts 82 made of transparent conductivefilms electrically connected in common. The upper electrode 8 has a slitshape, and includes each gap part 81 between the branch electrode parts82. The gap parts 81 do not include transparent conductive films. Afringe electric field is generated between the branch electrode parts 82and the lower electrode 6, so as to drive the liquid crystal layer.

Although the detail will be described later, in the upper electrode 8according to the first exemplary embodiment, the branch electrode parts82 have a constant width, and the gap parts 81 have different widths inthe direction of the scan line 2 (horizontal direction in FIG. 2).

As shown in FIGS. 2 and 3, the upper electrode 8 is connected to thecommon line 21 through a contact hole 9, and serves as the opposedelectrode of the reference potential. The upper electrode 8 which isformed of a transparent conductive film such as ITO has larger specificresistance compared with the scan line 2 or the signal line 5 which isformed of a metal film. Thus, the upper electrode 8 is connected to thecommon line 21 which is formed in the same layer as the scan line 2 foreach pixel 30, so as to achieve low resistance.

Furthermore, in the first exemplary embodiment, connection parts 85 and86, which are formed integrally with the upper electrode 8 in the samelayer, are formed above the direction of the signal lines 5 (verticaldirection in FIG. 2) and the direction of the scan lines 2,respectively. Furthermore, the upper electrode 8 and upper electrodes 8a of adjacent pixels 30 a are connected each other by the connectionparts 85 and 86. The connection parts 85 and 86 cover substantially thewhole part of the scan lines 2 and the signal lines 5, and are formed ina lattice (mesh) shape, so as to make the resistance of the upperelectrodes 8 and 8 a further lower.

Since the connection parts 85 and 86 are formed in a lattice shape, evenwhen the common line 21 is disconnected and no reference potential issupplied from the common line 21 to the upper electrode 8, the referencepotential is supplied to the upper electrode 8 from the upper electrodes8 a in the adjacent pixels 30 a through the connection parts 85 and 86.Thus, it is possible to prevent a display defect and to improve theyield rate.

Further, since a leakage electric field from the scan lines 2 or thesignal lines 5 to the liquid crystal layer can be shielded by coveringthe scan lines 2 or the signal lines 5 with the connection parts 85 and86, a display defect due to the leakage electric field that tends to begenerated near the scan lines 2 or the signal lines 5 can be suppressed.Further, in the color filter substrate 20, it is also possible toeliminate the light-shielding film along with the scan lines 2 or thesignal lines 5.

Note that the connection parts 85 and 86 may be formed above either ofthe signal lines 5 and the scan lines 2, so as to connect between theupper electrode 8 and the upper electrodes 8 a in the adjacent pixels 30a.

Next, the detail of the upper electrode 8 of the first exemplaryembodiment will be described. FIG. 5 is a plane view showing a main partof the upper electrode of the liquid crystal display device according tothe first exemplary embodiment. A main part 80 of the upper electrode 8is the part having substantially the same size as the lower electrode 6.

The reason why the upper electrode 8 is described with the main part 80is that, since the upper electrode 8 is connected to the upperelectrodes 8 a of the adjacent pixels 30 a through the connection parts85 and 86, the boundary between the upper electrode 8 and the connectionparts 85 and 86 is not clear. Another reason is that it is preferablethat the upper electrode 8 is described with the main part 80 also inconsideration of the functional aspect that the upper electrode 8 is anelectrode part that mainly contributes to the display. In the followingdescription, the upper electrode 8 indicates the main part 80 which hasbasically the same size as the lower electrode 6 and serves as anelectrode part which mainly contributes to the display.

As shown in FIG. 5, in the first exemplary embodiment, the upperelectrode 8 includes regions S2 and S3 arranged in the direction of thescan line 2. In the regions S2 and S3, widths W2 and W3 of the branchelectrode parts 82 that are provided inside with the exception for theouter peripheral part are the same (W2=W3), and widths C2 and C3 of thegap parts 81 are different. The widths of the gap parts 81 and thebranch electrode parts 82 have a constant linear shape, respectively.

Note that the width of the branch electrode part 82 in the outerperipheral part of the upper electrode 8 is excluded from theconstitutional condition of the present invention.

This is because, as stated above, since the connection part 85 isprovided, the width of the branch electrode part 82 in the outerperipheral part of the upper electrode 8 may not be clear. Anotherreason is that, even when there is no connection part 85 and the upperelectrode 8 does not overlap with the signal line 5, only the width ofthe branch electrode part 82 in the outer peripheral part of the upperelectrode 8 may be made larger than the width of the inner branchelectrode parts 82 in consideration of an overlay error of thelight-shielding film in the color filter substrate 20 in order toprevent light leakage from a gap between the upper electrode 8 and thesignal line 5.

From the above description, the first exemplary embodiment has a regionS in which the ratio R (=C/W) of the width C of the gap part 81 to thewidth W of the branch electrode part 82, which is adjacent to the gappart 81, varies with the exception for the outer peripheral part of theupper electrode 8. Further, the constitutional condition of the presentinvention has the following characteristics.

The upper electrode 8 in the pixel 30 is formed so as to include both ofa region S in which the light transmittance T increases and a region Sin which the light transmittance T decreases with respect to the changeof the ratio R. In summary, the upper electrode 8 in the pixel 30 isformed so as to cancel the increase and the decrease of the lighttransmittance T due to the variations in dimension of the arraymanufacturing process.

Next, operations and effects of the present invention will be describedin detail with reference to FIGS. 6, 7, and 8. FIG. 6 is a calculationdiagram showing one example of relations between light transmittancesand ratios of the width of the gap part to the width of the adjacentbranch electrode part of the upper electrode of the liquid crystaldisplay device according to the first exemplary embodiment. FIG. 7 is aview showing a relation between a light transmittance and a ratio of thewidth of the gap part to the width of the adjacent branch electrode partof the upper electrode of the liquid crystal display device according tothe first exemplary embodiment. FIG. 8 is a view showing relationsbetween light transmittances and ratios when the ratio shown in FIG. 7varies.

Note that the light transmittance T is not constant even in the region Sof the ratio R, but is varied according to the positions of the gap part81 and the branch electrode part 82. Thus, the light transmittance Tindicates an average value of the ratio R in the region S. The lighttransmittance T normalizes the maximum light transmittance as 100%.

As shown in the calculation diagram in FIG. 6, the light transmittancesT in the FFS-type liquid crystal display device 100 indicate thecalculation results of inversed-U shape including the ratio R1indicating the light transmittance T1 of the maximum value with respectto the ratio R (=C/W) of the width C of the gap part 81 to the width Wof the adjacent branch electrode part 82 of the upper electrode 8. Inthe calculation example shown in FIG. 6, the transmission rates T of thefive ratios R are calculated when the width W of the branch electrodeparts 82 is fixed to be 3 μm and the widths C of the adjacent gap parts81 vary between 4.5 to 6.75 μm. In the calculation example shown in FIG.6, calculation is performed under the voltage condition in which thelight transmittances T in the intermediate gradation are about 50%,where the display unevenness is easily recognized.

The value of the ratio R1 indicating the light transmittance T1 of themaximum value also depends on the display gradation, the material of theliquid crystal layer, the thickness of the liquid crystal layer, thethickness of the protection film, the width C of the gap part 81, thewidth W of the branch electrode part 82 of the upper electrode 8 or thelike.

In the conventional FFS-type liquid crystal display device 100, theplurality of gap parts 81 have the constant width C and the branchelectrode parts 82 have the constant width W with the exception for theouter peripheral part of the upper electrode 8, and the design isgenerally made by one ratio R.

However, in reality, there are generated variations in dimension in thewidth C of the gap part 81 and the width W of the branch electrode part82, which is adjacent to the gap part 81, in the array manufacturingprocesses including an exposure process and an etching process. As aresult, the ratio R of the width C of the gap part 81 to the width W ofthe branch electrode part 82 which is adjacent to the gap part 81varies. As shown from FIG. 7, in the case the upper electrode 8 isdesigned to have only one ratio R, the light transmittance T changeswhen the ratio R varies by dimensions variation.

Accordingly, when there are variations in dimension in the width C ofthe gap part 81 and the width W of the branch electrode part 82 that isadjacent to the gap part 81 in a part of the display area 50, the ratioR varies. Thus, the light transmittance T varies, and the displayunevenness of the liquid crystal display device 100 can be easilyrecognized.

Strictly speaking, the display unevenness is determined not only by thelight transmittance T but is recognized as the variation of the lighttransmission amount M obtained by multiplying the light transmittance Tby the area of the region S of the light transmittance T.

On the other hand, in the first exemplary embodiment, as shown in FIGS.5 and 7, while the widths W2 and W3 of the branch electrode parts 82 ofthe upper electrode 8 are the same (W2=W3), there are two kinds ofwidths C2 and C3 of the adjacent gap parts 81. Thus, the upper electrode8 includes two kinds of regions S2 and S3 of the ratios R2 (=C2/W2) andR3 (=C3/W3). For example, in FIG. 7, the ratios R2 and R3 satisfy theexpression R2<R1<R3, and the light transmittances T2, T3 of the regionsS2 and S3 corresponding to the ratios R2 and R3, respectively, aresomewhat smaller than the light transmittance T1 of the maximum value.

Next, with reference to FIG. 8, description will be made of a case inwhich the ratios R2 and R3 of the regions S2 and S3 of the upperelectrode 8 are increased by ratio change amounts ΔR2 and ΔR3,respectively, to the ratios R2 b and R3 b in a part including thedisplay area 50 due to the variations in dimension in the arraymanufacturing process. This case includes, for example, an example inwhich the widths C2 and C3 of the gap part 81 of the upper electrode 8increase and the widths W2 and W3 of the branch electrode part 82 of theupper electrode 8 decrease due to overexposure, overetching or the like.Note that the ratio change amount ΔR is not necessarily the same evenwhen constant dimensional changes are generated in the widths C2 and C3of the gap parts 81 and the widths W2 and W3 of the branch electrodeparts 82.

In FIG. 8, the region S2 of the ratio R2 satisfies the expression R2b=R2+ΔR2, which means that the light transmittance T2 is increased tothe light transmittance T2 b. Meanwhile, the region S3 of the ratio R3satisfies the expression R3 b=R3+ΔR3, which means that the lighttransmittance T3 is decreased to the light transmittance T3 b. From thedescription above, the upper electrode 8 includes both of the region S2where the transmission rate T increases and the region S3 where thetransmission rate T decreases with respect to the change of the ratio R.The light transmission amount M of the pixel 30 is obtained by addingthe result obtained by multiplying the light transmittance T2 b by thearea of the region S2 and the result obtained by multiplying the lighttransmittance T3 b by the area of the region S3.

The change in the light transmission amount M of the pixel 30 isobtained by adding the result obtained by multiplying the increase ofthe light transmittance T (T2 b−T2) by the area of the region S2 and theresult obtained by multiplying the decrease of the light transmittance T(T3−T3 b) by the area of the region S3. Accordingly, the increase andthe decrease of the light transmission amount M cancel with each other,thereby making it possible to decrease the change of the lighttransmission amount M of the pixel 30, and to suppress displayunevenness in the liquid crystal display device 100 due to variations indimension of the array manufacturing process.

In particular, it is preferable to design the ratios R2 and R3, and theareas of the regions S2 and S3 so as to make the increased amount andthe decreased amount of the light transmission amount M of the pixel 30due to the variations in dimension of the array manufacturing processsubstantially equal to each other. Accordingly, there is little changein the light transmission amount M of the pixel 30, thereby making itpossible to cancel the display unevenness of the liquid crystal displaydevice 100 due to the variations in dimension of the array manufacturingprocess.

The example stated above is the case in which the ratio R increases.However, the increase and the decrease of the light transmittances T2and T3 of the regions S2 and S3 cancel with each other also when theratio R decreases. In this case, the increase and the decrease arereversed. Thus, in this case as well, the display unevenness of theliquid crystal display device 100 due to the variations in dimension ofthe array manufacturing process can be suppressed.

Second Exemplary Embodiment

FIG. 9 is an enlarged plane view showing a pixel of a display area of aliquid crystal display device according to a second exemplaryembodiment. Although the width W of the branch electrode parts 82 ismade constant (W2=W3) in the first exemplary embodiment, in the secondexemplary embodiment, the width C of the gap parts 81 of the upperelectrode 8 is made constant (C2=C3), the widths W2 and W3 of the branchelectrode parts 82 are made different, and two kinds of regions S2 andS3 corresponding to the ratios R2 (=C2/W2) and R3 (=C3/W3) are arrangedin the direction of the scan line 2 (horizontal direction in FIG. 9).

The pixel 30 according to the second exemplary embodiment also includes,as is similar to the first exemplary embodiment, the region S in whichthe light transmittance T increases and the region S in which the lighttransmittance T decreases due to the change in the ratio R. Thus, thesame advantageous effects as in the first exemplary embodiment can beobtained. In particular, it is preferable to design the ratios R2 andR3, and the areas of the regions S2 and S3 are designed so as to makethe increased amount and the decreased amount of the light transmissionamount M substantially equal to each other. As a result, there is littlechange in the light transmission amount M of the pixel 30, therebymaking it possible to cancel the display unevenness of the liquidcrystal display device 100 due to variations in dimension of the arraymanufacturing process.

Third Exemplary Embodiment

FIG. 10 is an enlarged plane view showing a pixel of a display area of aliquid crystal display device according to a third exemplary embodiment.In the first and the second exemplary embodiments, the width C of thegap part 81 or the width W of the branch electrode part 82 of the upperelectrode 8 has a constant linear shape, respectively. However, in thethird exemplary embodiment, although the widths of the branch electrodeparts 82 are constant (W2=W3), one gap part 81 has different widths C2and C3. Furthermore, the gap parts 81 are arranged to be alternatelyvertically symmetrical in the direction of the scan line 2 (horizontaldirection in FIG. 10).

The pixel 30 according to the third exemplary embodiment also includes,as is similar to the first and the second exemplary embodiments, both ofthe region S in which the light transmittance T increases and the regionS in which the light transmittance T decreases due to the change in theratio R. Thus, the same advantageous effects as in the first exemplaryembodiment can be obtained. In particular, it is preferable to designthe ratios R2 and R3, and the areas of the regions S2 and S3 aredesigned so as to make the increased amount and the decreased amount ofthe light transmission amount M substantially equal to each other. As aresult, there is little change in the light transmission amount M of thepixel 30, thereby making it possible to cancel the display unevenness ofthe liquid crystal display device 100 due to variations in dimension ofthe array manufacturing process.

Fourth Exemplary Embodiment

FIG. 11 is an enlarged plane view showing a pixel of a display area of aliquid crystal display device according to a fourth exemplaryembodiment. While the gap parts 81 are arranged to be alternatelyvertically symmetrical in the direction of the scan line 2 (horizontaldirection in FIG. 10) in the third exemplary embodiment, the gap parts81 are arranged in the same shape in the direction of the scan line 2(horizontal direction in FIG. 11) in the fourth exemplary embodiment.

Although the widths C2 and C3 of the gap part 81 and the widths W2 andW3 of the branch electrode part 82, which is adjacent to the gap part81, are different from each other, the sum P of the widths C2 and C3 ofthe gap part 81 and the widths W2 and W3 of the branch electrode part 82in each of the regions S2 and S3 is constant so as to satisfyP=C2+W2=C3+W3.

The connection parts 85 and 86 that are connected to the upper electrode8 cover substantially the whole part of the scan line 2 and the signalline 5 in the first to third exemplary embodiments. Meanwhile, in thefourth exemplary embodiment, the connection parts 85 and 86 are formedto cover substantially the whole width of the scan line 2 and the signalline 5 with the exception for the TFT region T. Accordingly, it ispossible to suppress the influence given on the ON/OFF characteristicsof the TFT by the potentials of the connection parts 85 and 86 connectedto the upper electrode 8.

As is similar to the first to third exemplary embodiments, the fourthexemplary embodiment also includes in the pixel 30, both of the region Sin which the light transmittance T increases and the region S in whichthe light transmittance T decreases due to the change of the ratio R.Thus, the same advantageous effects as in the first exemplary embodimentcan be obtained. In particular, it is preferable to design the ratios R2and R3, and the areas of the regions S2 and S3 are designed so as tomake the increased amount and the decreased amount of the lighttransmission amount M substantially equal to each other. As a result,there is little change in the light transmission amount M of the pixel30, thereby making it possible to cancel the display unevenness of theliquid crystal display device 100 due to variations in dimension of thearray manufacturing process.

Fifth Exemplary Embodiment

FIG. 12 is an enlarged plane view showing a pixel of a display area of aliquid crystal display device according to a fifth exemplary embodiment.In the fifth exemplary embodiment, as is similar to the first exemplaryembodiment, while the widths W2 and W3 of the branch electrode parts 82are the same (W2=W3), the widths C2 and C3 of the gap parts 81 aredifferent. Then, the widths C2 and C3 of the gap parts 81 arealternately arranged in the direction of the scan line 2 (horizontaldirection in FIG. 11). The widths of the gap part 81 and the branchelectrode part 82 have constant linear shape. In short, the regions S2and S3 of the ratios R2 (=C2/W2) and R3 (=C3/W3) is alternatelyarranged.

Further, in the fifth exemplary embodiment, the connection parts 85 and86 connected to the upper electrode 8 are formed so as to cover only onepart of the scan line 2 and the signal line 5. In this case, an increasein the parasitic capacitance of the scan line 2 or the signal line 5 canbe suppressed although the shielding effect of the leakage electricfield from the scan line 2 or the signal line 5 by the connection parts85 and 86 decreases. Further, it is possible to suppress occurrence ofthe short-circuit of the connection part 85 and the signal line 5 due tothe film detect of the protection film 7 or the short-circuit of theconnection part 86 and the scan line 2 due to the film detects of thegate insulation film 3 and the protection film 7.

The pixel 30 according to the fifth exemplary embodiment also includes,as is similar to the first to fourth exemplary embodiments, both of theregion S in which the light transmittance T increases and the region Sin which the light transmittance T decreases due to the change of theratio R. Thus, the same advantageous effects as in the first exemplaryembodiment can be obtained. In particular, it is preferable to designthe ratios R2 and R3, and the areas of the regions S2 and S3 aredesigned so as to make the increased amount and the decreased amount ofthe light transmission amount M substantially equal to each other. As aresult, there is little change in the light transmission amount M of thepixel 30, thereby making it possible to cancel the display unevenness ofthe liquid crystal display device 100 due to variations in dimension ofthe array manufacturing process.

Sixth Exemplary Embodiment

FIG. 13 is a plane view showing an upper electrode and a lower electrodeof a liquid crystal display device according to a sixth exemplaryembodiment. In the sixth exemplary embodiment, the lower electrode 6 isthe opposed electrode, and the upper electrode 8 is the pixel electrode.Then the shape of the upper electrode 8 is a comb-tooth shape in whichat least one end of each of the gap parts 81 is opened.

In this case, the upper electrode 8 which is the pixel electrode isconnected to the drain electrode (not shown), and is separated from theupper electrode of the adjacent pixel. The lower electrode 6 isconnected to a common line (not shown) of a reference potential.

Further, even when the upper electrode 8 has a comb-tooth shape, thelower electrode 6 may be a pixel electrode and the upper electrode 8 maybe an opposed electrode. In this case, as in the first to fifthexemplary embodiments, the upper electrode can be connected to the upperelectrode 8 of the adjacent pixel through the connection part.

As is similar to the first and fifth exemplary embodiments, in the sixthexemplary embodiment, while the widths W2 and W3 of the branch electrodeparts 82 are constant (W2=W3), the widths C2 and C3 of the adjacent gapparts 81 are different. The widths C2 and C3 of the gap part 81 arealternately arranged in the direction of the scan line 2 (horizontaldirection in FIG. 13). Each width of the gap part 81 and the branchelectrode part 82 has a constant linear shape. In summary, the regionsS2 and S3 of the ratios R2 (=C2/W2) and R3 (=C3/W3) is alternatelyarranged.

One end of each of the gap parts 81 shown by a dotted region G is openedby changing the shape of the upper electrode 8 from a slit shape to acomb-tooth shape. Accordingly, the lower electrode 6 is exposed also inthis region G and the fringe electric field can be applied moreeffectively, thereby increasing the light transmission amount M.

The pixel 30 according to the sixth exemplary embodiment also includes,as is similar to the first to fifth exemplary embodiments, both of theregion S in which the light transmittance T increases and the region Sin which the light transmittance T decreases due to the change of theratio R. Thus, the same advantageous effects as in the first exemplaryembodiment can be obtained. In particular, it is preferable to designthe ratios R2 and R3, and the areas of the regions S2 and S3 aredesigned so as to make the increased amount and the decreased amount ofthe light transmission amount M substantially equal to each other. As aresult, there is little change in the light transmission amount M of thepixel 30, thereby making it possible to cancel the display unevenness ofthe liquid crystal display device 100 due to variations in dimension ofthe array manufacturing process.

Seventh Exemplary Embodiment

FIG. 14 is a plane view showing an upper electrode and a lower electrodeof a liquid crystal display device according to a seventh exemplaryembodiment. As is similar to the sixth exemplary embodiment, the seventhexemplary embodiment includes the lower electrode 6 which is the opposedelectrode and the upper electrode 8 which is the pixel electrode.Further, the upper electrode 8 has a comb-tooth shape having at leastone end of each of the gap parts 81 opened.

As is similar to the fourth exemplary embodiment, the seventh exemplaryembodiment has two different kinds of widths C2 and C3 in one gap part81, and the regions S2 and S3 having the widths W2, W3 of thecorresponding branch electrode part 82 are arranged in the direction ofthe signal line 5 (vertical direction in FIG. 14). Although the widthsC2, C3 of the gap part 81 and the widths W2, W3 of the branch electrodepart 82 are different from each other, the sum P of the widths C2 and C3of the gap part 81 and the widths W2 and W3 of the branch electrode part82 in the regions S2 and S3 is constant and expressed as P=C2+W2=C3+W3.

The pixel 30 according to the seventh exemplary embodiment also includesin, as is similar to the first to sixth exemplary embodiments, both ofthe region S in which the light transmittance T increases and the regionS in which the light transmittance T decreases due to the change of theratio R. Thus, the same advantageous effects as in the first exemplaryembodiment can be obtained. In particular, it is preferable to designthe ratios R2 and R3, and the areas of the regions S2 and S3 aredesigned so as to make the increased amount and the decreased amount ofthe light transmission amount M substantially equal to each other. As aresult, there is little change in the light transmission amount M of thepixel 30, thereby making it possible to cancel the display unevenness ofthe liquid crystal display device 100 due to variations in dimension ofthe array manufacturing process.

Although the upper electrode 8 has two kinds of ratios R (=C/W) in theabove exemplary embodiments, the upper electrode 8 may have three ormore kinds of ratios R. For example, even when there are n kinds ofregions S having different ratios R, the upper electrode 8 has both ofthe region S in which the light transmittance T increases and the regionS in which the light transmittance T decreases with respect to thechange in the ratio R. In particularly, n kinds of ratios R and the areaof each region S may be designed and arranged so as to make theincreased amount and the decreased amount of the light transmissionamount M in the pixel 30 substantially equal to each other.

Furthermore, the branch electrode part 82 or the gap part 81 of theupper electrode 8 may have a step-like shape or a concavo-convex shapewith changes of two or more widths. Alternatively, the shape may be atriangular shape or a trapezoidal shape with successive changes inwidths. Further alternatively, the shape may be other shape than thestraight line shape, but may be a zigzag shape or a curved shape.

Furthermore, while the gap part 81 and the branch electrode part 82 ofthe upper electrode 8 are arranged in the direction of the signal line 5(vertical direction in the drawing) in the above exemplary embodiments,they may be arranged in the direction of the scan line 2 (horizontaldirection in the drawing). Alternatively, they may be arranged in anoblique direction with respect to the direction of the scan line 2(horizontal direction in the drawing) or the direction of the signalline 5 (vertical direction in the drawing).

Although the TFT has a channel etch inverted staggered structure in theexemplary embodiments described above, the TFT may be applied to aliquid crystal display device employing a TFT of etch stopper invertedstaggered type or top gate type.

Although the drive circuit is mounted with the COG mounting technique inthe exemplary embodiments described above, the drive circuit may beapplied to a drive circuit that is mounted with the TAB (Tape AutomatedBonding) mounting technique, Furthermore, the drive circuit may be hadbuilt-in by forming TFTs for the driver circuit on the array substrate.

From the invention thus described, it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

What is claimed is:
 1. A liquid crystal display device comprising: apair of substrates; a liquid crystal layer that is sealed between thesubstrates; and a display area comprising a plurality of pixels arrangedtherein in matrix on one of the substrates, the pixels being defined byscan lines and signal lines that cross with the scan lines, wherein eachof the pixels comprises a switching element, a lower electrode, and anupper electrode that is arranged on the lower electrode with aninsulation film interposed therebetween, the upper electrode comprises aplurality of branch electrode parts electrically connected in common,and a gap part between the branch electrode parts, the upper electrodecomprises a first region of a pixel wherein a ratio of a width of thegap part to a width of the branch electrode part that is adjacent to thegap part is a first value and a second region of said pixel wherein aratio of a width of the gap part to a width of the branch electrode partthat is adjacent to the gap part is a second value, wherein the secondvalue is different from the first value, and the upper electrodecomprises both of a region in which a light transmittance increases, thelight transmittance increasing when the ratio of the width of the gappart to the width of the branch electrode part that is adjacent to thegap increases to a first range ratio that is less than a predeterminedthreshold ratio, and a region in which the light transmittancedecreases, the light transmittance decreasing when the ratio of thewidth of the gap part to the width of the branch electrode part that isadjacent to the gap increases to a second range ratio that is greaterthan the predetermined threshold ratio.
 2. The liquid crystal displaydevice according to claim 1, wherein an increased amount of a lighttransmission amount of a region in which the light transmittanceincreases and a decreased amount of a light transmission amount of aregion in which the light transmittance decreases are substantiallyequal to each other, only in a vicinity of the predetermined thresholdratio.
 3. The liquid crystal display device according to claim 2,wherein the upper electrode comprises a region in which the width of atleast one of the gap parts or the branch electrode parts is notconstant.
 4. The liquid crystal display device according to claim 2,wherein the upper electrode comprises a region in which the width of atleast one of the gap parts is different from the width of the other gapparts.
 5. The liquid crystal display device according to claim 2,wherein the upper electrode comprises a region in which the width of atleast one of the branch electrode parts is different from the width ofthe other branch electrode parts.
 6. The liquid crystal display deviceaccording to claim 1, wherein the upper electrode comprises a region inwhich the width of at least one of the gap parts or the branch electrodeparts is not constant.
 7. The liquid crystal display device according toclaim 1, wherein the upper electrode comprises a region in which thewidth of at least one of the gap parts is different from the width ofthe other gap parts.
 8. The liquid crystal display device according toclaim 1, wherein the upper electrode comprises a region in which thewidth of at least one of the branch electrode parts is different fromthe width of the other branch electrode parts.
 9. The liquid crystaldisplay device according to claim 1, wherein the plurality of gap partsor branch electrode parts of the upper electrode are arranged to bealternately symmetrical with respect to the vertical or horizontaldirection of a pixel in a planar view.
 10. The liquid crystal displaydevice according to claim 1, wherein the upper electrode has acomb-tooth shape in which one end of each of the gap parts is opened ina planar view.
 11. The liquid crystal display device according to claim1, wherein the upper electrode is an opposed electrode which is areference potential, and the lower electrode is a pixel electrode whichis connected to a switching element.
 12. The liquid crystal displaydevice according to claim 11, wherein a connection part connected to theupper electrode is connected to the upper electrode of an adjacent pixelin the vertical or horizontal direction.
 13. The liquid crystal displaydevice according to claim 12, wherein a connection part connected to theupper electrode has a shape so as to cover substantially the whole widthof the scan line or the signal line.
 14. The liquid crystal displaydevice according to claim 12, wherein the connection part connected tothe upper electrode has a shape so as to cover substantially the wholewidth of the scan line and the signal line with the exception for aregion of the switching element.
 15. The liquid crystal display deviceaccording to claim 11, wherein the upper electrode is connected to acommon line that is provided in the same layer as the scan line througha contact hole provided in an insulation film in each pixel.
 16. Theliquid crystal display device according to claim 11, wherein the lowerelectrode is disposed in an entire area located below the gap part. 17.The liquid crystal display device according to claim 1, wherein aninstantaneous rate at which the light transmittance increases isproportional to an increase in difference between the first range ratioand the predetermined threshold ratio.
 18. The liquid crystal displaydevice according to claim 1, wherein an instantaneous rate at which thelight transmittance decreases is proportional to an increase indifference between the second range ratio and the predeterminedthreshold ratio.
 19. The liquid crystal display device according toclaim 1, wherein the light transmittance reaches a maximum value at thepredetermined threshold ratio.
 20. The liquid crystal display deviceaccording to claim 1, wherein an instantaneous rate at which the lighttransmittance increases at the predetermined threshold ratio issubstantially zero, and an instantaneous rate at which the lighttransmittance decreases at the predetermined threshold ratio issubstantially zero.